5a_Flip_Flop_Review_Slides

5a_Flip_Flop_Review_Slides - ECE ECE 3534 Digital Design 1...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ECE ECE 3534 Digital Design 1 Section 5a: Review of Flip-Flops Flip Flip-Flops • We can describe flip-flops in terms We of their characteristic information. • Characteristic information describes the next state of the flipflop as a function of the present state and all of the flip-flop inputs. • Instead of considering the operation of the flip-flop in terms of all of the distinct combinations ll di of input and present state, we can describe the flip-flop in terms of the functions that each combination of the inputs carries out. The The SR Flip-Flop S 0 0 1 1 R 0 1 0 1 Q Q+ 0 1 0 1 0 1 0 1 Function The characteristic equation for the SR flip flip-flop is Q+ = S + R′Q, but this but characteristic equation only applies for valid values of S and R. The The D Flip-Flop Imagine Imagine that an SR flip flop has had its S and R inputs connected through an inverter. Call the new input D. S 0 1 R 1 0 D 0 1 Q Q+ 0 1 0 1 Function The characteristic equation of the D flip-flop is Q+ = D. The The JK Flip-Flop Consider Consider the JK flip-flop as an improved SR flip-flop. Unlike the SR flip-flop, the input J = K = 1 has a valid function. lid J 0 0 1 1 K 0 1 0 1 Q Q+ 0 1 0 1 0 1 0 1 Function The characteristic equation for the JK JK flip-flop is Q+ = JQ′ + K′Q. The The T Flip-Flop Imagine Imagine that a JK flip flop has had its inputs connected. Call the new input T. J 0 1 K 0 1 T 0 1 Q Q+ 0 1 0 1 Function The characteristic equation for the T flip-flop is Q+ = T ⊕ Q. Flip Flip-Flops • Characteristic information answers Characteristic the question “Based on the present information, what will the next state be?” • This information is important, but it doesn’t answer an important design question. Generally, we know what the present state is and what the next state should be. • Our question is “Given a known present state, and a desired next state, what do the flip-flop inputs have to be to achieve the state transition? transition?” Excitation Excitation Information • This information is called excitation This information. • We can derive the excitation information for each flip-flop by reorganizing its characteristic information. • If we consider the transitions as functions, we can determine which functions of the flip-flop achieve fli each transition. Excitation Excitation Information SR flip-flop • Functions: no change, set, reset Function? Q 0 0 1 1 Q+ 0 1 0 1 S R Excitation Excitation Information D flip-flop • Functions: set, reset Function? Q 0 0 1 1 Q+ 0 1 0 1 D Excitation Excitation Information JK flip-flop • Functions: no change, set, reset, toggle Function? Q 0 0 1 1 Q+ 0 1 0 1 J K Excitation Excitation Information T flip-flop • Functions: no change, toggle Function? Q 0 0 1 1 Q+ 0 1 0 1 T ...
View Full Document

Ask a homework question - tutors are online